Vibrations are applied to the mold in continuous casting equipment by a vibrating apparatus. A known vibrating apparatus of this type is disclosed in Japanese Patent Application Kokai No. 63562/1988.
In this vibrating apparatus, the mold is supported for upward and downward movements in a vertical plane through a four-bar link and a beam, with a hydraulic cylinder connected to the front end of said beam for vibrating the mold. The hydraulic circuit for feeding said hydraulic cylinder with hydraulic pressure is provided with a servo valve and a control circuit for controlling said servo valve.
In this control circuit, the rod position of the hydraulic cylinder and the acceleration of the mold are detected by respective sensors. It is arranged that the individual detected values are fed back to improve the vibration transfer characteristic to allow the vibrations of the mold to take a predetermined vibration waveform.
The reason why the vibration transfer characteristic has to be improved in this manner is as follows.
Attempts have recently been made to generate in the mold a saw-tooth vibration waveform adapted to increase and decrease the upward and downward movements of the mold, respectively, so as to improve the quality of the surfaces of castings produced by continuous casting. Such saw-tooth non-sinusoidal waveform contains harmonic wave components, such as second and third. And under certain vibrating conditions, the mechanical support structure including beams for supporting the entire mold resonates with such harmonic wave components, making it impossible to obtain a predetermined vibration waveform. Therefore, the attempts are intended to prevent the occurrence of such phenomena.
In this connection, it is to be noted that the above arrangement is based on the principle of detecting the Pod position of the hydraulic cylinder and the acceleration of the mold, and feeding back these detected values so as to obtain a predetermined vibration waveform. However, since the subject of control is complicated and the sensor attaching locations are limited, there is a problem that a predetermined vibration waveform is hard to obtain.
Further, in continuous casting equipment, since the environmental conditions are poor, the sensors tend to break down. Therefore, if a sensor breaks down, the hydraulic cylinder runs away and hence the vibration has to be stopped. That is, it is necessary to stop casting, thus offering a problem that waste is involved as the molten metal has to be brought back into the ladle and scrap formation takes place.